1. Field of the Invention
This invention relates to packaging of semiconductor chips and more particularly to line-to-via connections in ceramic packaging structures.
2. Description of Related Art
In current multilayered ceramic packaging, the conductor lines are being narrowed in an attempt to maximize the use of space on the package to increase the density of the package.
The problem addressed here is that in view of the narrowness of the circuit conductors and the mechanics of formation of multilayered glass ceramic packages, there is a tendency for line-to-via cracking opens defects to appear where thin conductor lines are joined to large vias. One possible problem is that large copper grains are employed. In addition, opens are caused by contamination and line thinning at line-to-via junctions.
In FIG. 1, a multilayered ceramic package 10 has a set of vias 11, 12, 13 connected in turn to lines 14, 15, 16 with conductor lines 14-16 being very narrow, i.e. only about 76 .mu.m (3 mils) wide. As can be seen the vias are far larger in width than the conductor lines and a problem of cracking at the junction or interface between the line and the via leads to open circuits to an undesirable degree.
FIG. 3A is a plan view of a segment of the prior art package of FIG. 1 rotated 90.degree.. FIG. 3B is a section of FIG. 3A taken along line 3B--3B showing the thickness of prior art line-to-via connections. FIG. 3A and FIG. 3B show a fragment of the plan and sectional schematics of the package FIG. 1 with one of the prior art line to via connections of FIG. 1. The via 12 of FIG. 1 is connected in turn to line 14 with conductor lines 15 being thin, having a thickness t.sub.1 only about 12 .mu.m (0.5 mil) thick.
In accordance with this invention, a semiconductor ceramic packaging substrate has vias of sintered electrically conductive metal therethrough and metal conductive elements on the surface thereof. The vias are connected to the conductive elements in a predetermined pattern. The improvement comprises a via having a conductive cap on the surface thereof. The conductive cap joins the via and the conductive element. The cap has a width substantially larger than the diameter of the vias at the point of contact of each of the vias and the associated conductor in contact therewith.
Further in accordance with this invention, a semiconductor glass ceramic packaging substrate has vias of sintered electrically conductive metal therethrough and metal conductive elements on the surface thereof. The vias are connected to the conductive elements in a predetermined pattern. The improvement comprises the via having a conductive cap on the surface thereof. The cap joins the via and the conductive element. The conductive cap has a width on the order of 1.5 to 2 times the diameter of the vias at the point of contact of each of the vias and the associated conductor in contact therewith.
In semiconductor ceramic packaging substrates having vias of sintered electrically conductive metal therethrough and metal conductive elements on the surface thereof, the vias are connected to the conductive elements in a predetermined pattern. The improvement comprises a conductive via cap on the surface of the via. The via cap has a cross sectional area substantially larger than the cross sectional area of the conductive element at the point of contact of the via cap and the conductive element in contact therewith.
In summary, a semiconductor ceramic packaging substrate has the usual vias of sintered electrically conductive metal extending through the substrate. There are the usual metal conductor lines comprising conductive elements on the surface of the substrate. Each via is connected to the conductive elements in a predetermined pattern through a conductive via cap on the surface of the ceramic package. The caps join each conductive element and each via. The cap has a width substantially larger than the diameter of the via at the point of contact of the via and the conductive element in contact with it. The caps are also substantially thicker and wider than the conductive elements.